60
Xiangning Chen et al. / Chinese Journal of Catalysis 36 (2015) 57–67
20
84.1, 77.8, 50.9, 45.6, 35.5, 27.4, 21.0. HRMS (ESI) Calcd. for
C23H27NO5 [M+Na]+: 420.1781; Found: 420.1786. Method a: 50
mg, 63% yield, 89% ee; [α]D20 = –30.0 (c 0.30, CHCl3); Method
49 mg, 62% yield, –86% ee, [α]D = +19.6 (c 0.28, CHCl3);
20
Method c: 72 mg, 91% yield, –92% ee, [α]D = +22.1 (c 0.38,
CHCl3).
20
b: 51 mg, 64% yield, –80% ee, [α]D = +31.0 (c 0.26, CHCl3);
(3R,4R)‐tert‐Butyl‐3‐benzyl‐4‐(4‐methoxyphenyl)‐5‐nitro‐2‐
oxopentanoate (6ac). The title compound was prepared ac‐
cording to the general procedures described above and purified
by column chromatography to give a white solid. The ee values
of the product were determined by HPLC using a Chiralcel
OD‐H column (70:30 hexane:isopropanol, 1 mL/min, 254 nm,
25 °C; t1 = 14.4 min, t2 = 32.2 min) and the dr values were de‐
termined by H NMR to be >20:1 in all cases. H NMR (400
MHz, CDCl3): δ 7.17–7.27 (m, 3H), 7.11–7.14 (m, 4H), 6.82 (d, J
= 8.4 Hz, 2H), 4.67–4.80 (m, 2H), 4.15–4.21 (m, 1H), 3.83–3.89
(m, 1H), 3.75 (s, 3H), 2.98 (d, J = 8.0 Hz, 2H), 1.28 (s, 9H). 13C
NMR (100 MHz, CDCl3): δ 196.6, 159.3, 159.2, 137.2, 129.3,
129.0, 128.8, 128.5, 126.9, 114.4, 84.1, 78.1, 55.2, 50.9, 45.1,
20
Method c: 65 mg, 82% yield, –91% ee, [α]D = +32.3 (c 0.34,
CHCl3).
(3R,4R)‐tert‐Butyl‐3‐(3,4‐dichlorobenzyl)‐5‐nitro‐2‐oxo‐4‐
phenylpentanoate (6ca). The title compound was prepared
according to the general procedures described above and puri‐
fied by column chromatography to give a white solid. The ee
values of the product were determined by HPLC using a Chi‐
ralcel OD‐H column (80:20 hexane:isopropanol, 1 mL/min, 254
nm, 25 °C; t1 = 15.9 min, t2 = 18.7 min) and the dr values were
1
1
1
1
determined by H NMR to be >20:1 in all cases. H NMR (400
MHz, CDCl3): δ 7.26–7.34 (m, 4H), 7.20–7.22 (m, 3H), 6.92–6.95
(m, 1H), 4.79–4.80 (m, 2H), 4.14–4.20 (m, 1H), 3.90–3.95 (m,
1H), 2.94 (d, J = 8.0 Hz, 2H), 1.32 (s, 9H). 13C NMR (100 MHz,
CDCl3): δ 195.9, 159.3, 137.4, 136.3, 132.7, 131.1, 130.9, 130.7,
129.2, 128.5, 128.4, 128.1, 84.6, 77.4, 50.7, 45.5, 34.5, 27.4.
HRMS (ESI) Calcd. for C22H23Cl2NO5 [M+Na]+: 474.0845; Found:
36.0, 27.5. HRMS (ESI) Calcd. for C23H27NO6 [M+Na]+: 436.1731;
Found: 436.1721. Method a: 53 mg, 64% yield, 86% ee, [α]D
–26.9 (c 0.30, CHCl3); Method b: 52 mg, 63% yield, –80% ee,
[α]D = +26.3 (c 0.41, CHCl3,); Method c: 71 mg, 86% yield,
20
=
20
474.0848. Method a: 55 mg, 61% yield, 66% ee, [α]D20 = –10.4
–92% ee, [α]D20 = +28.7 (c 0.55, CHCl3).
20
(c 0.26, CHCl3); Method b: 61 mg, 68% yield, –86% ee, [α]D
=
(3R,4R)‐tert‐Butyl‐3‐benzyl‐4‐(4‐fluorophenyl)‐5‐nitro‐2‐
oxopentanoate (6ad). The title compound was prepared ac‐
cording to the general procedures described above and purified
by column chromatography to give a white solid. The ee values
were determined by HPLC using a Chiralcel OD‐H column
(70:30 hexane:isopropanol, 1 mL/min, 254 nm, 25 °C); t1 = 11.7
+13.8 (c 0.61, CHCl3); Method c: 73 mg, 81% yield, –92% ee,
[α]D20 = +12.0 (c 0.45, CHCl3).
(R)‐tert‐Butyl‐3‐((R)‐2‐nitro‐1‐phenylethyl)‐2‐oxo‐6‐phenyl‐
hexanoate (6da). The title compound was prepared according
to the general procedures described above and purified by
column chromatography to give a white solid. The ee values of
the products were determined by HPLC using a Chiralcel OD‐H
column (95:5 hexane:isopropanol, 1 mL/min, 254 nm, 25 °C; t1
= 23.5 min, t2 = 26.9 min) and the dr values were determined
by 1H NMR to be >20:1 in all cases. 1H NMR (400 MHz, CDCl3): δ
7.24–7.31 (m, 5H), 7.15–7.20 (m, 3H), 7.10–7.12 (m, 2H),
4.63–4.65 (m, 2H), 3.73–3.84 (m, 2H), 2.53–2.65 (m, 2H),
1.77–1.87 (m, 1H), 1.51–1.66 (m, 3H), 1.39 (s, 9H). 13C NMR
(100 MHz, CDCl3): δ 196.6, 160.3, 141.2, 136.9, 129.1, 128.5,
128.4, 128.1, 126.1, 84.4, 77.6, 49.6, 45.2, 35.5, 28.5, 28.4, 27.6.
HRMS (ESI) Calcd. for C24H29NO5 [M+Na]+: 434.1938; Found:
1
min, t2 = 32.8 min) and the dr values were determined by H
1
NMR to be >20:1 in all cases. H NMR (400 MHz, CDCl3): δ
7.18–7.29 (m, 5H), 7.11–7.13 (m, 2H), 6.97–7.01 (m, 2H),
4.78–4.83 (m, 1H), 4.68–4.74 (m, 1H), 4.17–4.24 (m, 1H),
3.88–3.94 (m, 1H), 2.96–2.99 (m, 2H), 1.28 (s, 9H). 13C NMR
(100 MHz, CDCl3): δ 196.4, 163.6, 161.2, 159.3, 136.8, 132.5,
132.4, 130.0, 129.9, 129.0, 128.9, 127.1, 116.1, 115.9, 84.3, 77.9,
50.6, 45.0, 36.1, 27.5; 19F NMR (376 MHz, CDCl3): –113.5. HRMS
(ESI) Calcd. for C22H24FNO5 [M+Na]+: 424.1531; Found:
424.1520. Method a: 28 mg, 35% yield, 87% ee, [α]D20 = –35.4
(c 0.44, CHCl3); Method b: 59 mg, 74% yield, –90% ee, [α]D
20
=
434.1947. Method a: 35 mg, 43% yield, 88% ee, [α]D20 = –15.1
+35.6 (c 0.44, CHCl3); Method c: 64 mg, 80% yield, –91% ee,
[α]D20 = +34.3(c 0.26, CHCl3).
20
(c 0.25, CHCl3); Method b: 68 mg, 83% yield, –84% ee, [α]D
=
+13.2(c 0.59, CHCl3); Method c: 58 mg, 71% yield, –91% ee,
[α]D20 = +15.5 (c 0.41, CHCl3).
(3R,4R)‐tert‐Butyl‐3‐benzyl‐4‐(4‐chlorophenyl)‐5‐nitro‐2‐
oxopentanoate (6ae). The title compound was prepared ac‐
cording to the general procedures described above and purified
by column chromatography to give a white solid. The ee values
of the product were determined by HPLC using a Chiralcel
OD‐H column (70:30 hexane:isopropanol, 1 mL/min, 254 nm,
25 °C; t1 = 13.4 min, t2 = 33.9 min) and the dr values were de‐
termined by H NMR to be >20:1 in all cases. H NMR (400
MHz, CDCl3): δ 7.25–7.29 (m, 4H), 7.15–7.23 (m, 3H), 7.11–7.13
(m, 2H), 4.78–4.82 (m, 1H), 4.68–4.74 (m, 1H), 4.17–4.23 (m,
1H), 3.87–3.93 (m, 1H), 2.96–2.98 (m, 2H), 1.29 (s, 9H). 13C
NMR (100 MHz, CDCl3): δ 196.3, 159.3, 136.7, 135.3, 134.2,
129.6, 129.3, 129.0, 128.9, 127.1, 84.4, 77.7, 50.5, 45.1, 36.0,
(3R,4R)‐tert‐Butyl‐3‐benzyl‐5‐nitro‐2‐oxo‐4‐p‐tolylpentano‐
ate (6ab). The title compound was prepared according to the
general procedures described above and purified by column
chromatography to give a white solid. The ee values of the
products were determined by HPLC using a Chiralcel OD‐H
column (70:30 hexane:isopropanol, 1 mL/min, 254 nm, 25 °C;
t1 = 11.3 min, t2 = 24.5 min) and the dr values were determined
by 1H NMR to be >20:1 in all cases. 1H NMR (400 MHz, CDCl3): δ
7.17–7.27 (m, 3H), 7.09–7.13 (m, 6H), 4.70–4.81 (m, 2H),
4.16–4.22 (m, 1H), 3.85–3.91 (m, 1H), 2.99 (d, J = 7.6 Hz, 2H),
2.28 (s, 3H), 1.28 (s, 9H). 13C NMR (100 MHz, CDCl3): δ 196.5,
159.3, 137.9, 137.2, 133.6, 129.8, 129.0, 128.8, 128.0, 126.9,
84.1, 77.9, 50.9, 45.4, 35.9, 27.4, 21.1. HRMS (ESI) Calcd. for
C23H27NO5 [M+Na]: 420.1781; Found: 420.1771. Method a: 36
mg, 44% yield, 91% ee, [α]D20 = –18.8 (c 0.17, CHCl3); Method b:
1
1
27.5. HRMS (ESI) Calcd. for C22H24ClNO5 [M+Na]+: 440.1235;
20
Found: 440.1234. Method a: 32 mg, 38% yield, 92% ee, [α]D
=
–26.2 (c 0.21, CHCl3); Method b: 40 mg, 48% yield, –91% ee,
20
[α]D = +25.9 (c 0.28, CHCl3); Method c: 65 mg, 78% yield,